Early Gas Trap Op Rod made by Springfield Armory. This is a Curved Side op rod made during the transition from the Slant Side SA-0 to the Curved Side SA-1. During this transition quite a number were produced that were not marked with the new drawing revision number. These Unmarked Op Rods were used from approx 22,000 to 33,000 and possibly futher. In Scott Duff's "The M1 Garand: World War II" page 198, Gas Trap rifle with serial 26171 can be seen with this same op rod with no drawing number. This op rod has a new piston measuring .5265, a lug measuring .097 and has the modification cut in the handle. The surface has been reparkerized, probably when the handle mod was done, and is at 95%+. with no rust and no pitting, this is a very nice op rod to complete your rifle.